When watching a scary movie alone at night, this system is likely to become engaged due to the perception of a threat; sudden noises are likely to cause an involuntary flight reaction that, of course, subsides after a moment. 8)

Temporal summation in a nerve cell occurs when the length of time over which successive activation potentials occur is sufficiently long enough to allow for the potentials to continue to the point where they begin to overlap. When this occurs, a new activation starts to begin before the climax of the preceding action potential has been reached. This action potential essentially ends prematurely, or summates, as it begins the rise into the next action potential, which ends up being larger in magnitude than the constituent action potentials. Summation of active potential in muscle fibers allows for similarly larger action potentials, which can increase the strength of the fiber contractions.

9)

There are two basic types of skeletal muscle fiber, Type I and Type II, or fast and slow. Type II fibers can be further subdivided by both size and speed. Basically, the larger a muscle fiber is, the faster its "twitch" or activation response time (i.e. The faster it contracts in response to a given amount of stimulus), and the faster it fatigues. Type I muscle fibers are slow twitch; they are slow to fatigue but also slow to move and do not produce as much power. Type II muscle fibers are larger and faster, producing more power but tiring faster as well.

10)

Peripheral fatigue involves the physical failure of muscles to carry out their typical functions, usually through a combination of muscle tissue and neurotransmitter inhibitors at the site of the muscle. Thus, periphery fatigue can be thought of as fatigue that occurs at the muscle site, and is usually the first type of fatigue to occur during extended muscle use. Initial muscle failures of muscle ability during a workout with multiple repetitions are an example of muscle fatigue; a depletion and/or imbalance of neurotransmitters is at least partially to blame for the inability of the muscle...

Central fatigue occurs along the central nervous system, and results from a similar depletion/imbalance of neurotransmitters and the ions that create resting and action potentials. This takes longer to occur, however; the eventual fatigue and overall weakness at the end of a workout is related more to central fatigue than simply to peripheral fatigue, and takes longer to "reset."
11)

Sleep begins with initial relaxation, when brain waves change from rapid beta waves to slower alpha waves. The first stage of true sleep occurs when alpha waves become theta waves, and the sleeper has almost no sensory perception. In stage two sleep, the heart rate slows still further, body temperature decreases, and the body prepares for deeper sleep. This sleep comes in stages three and four, where brain waves becomes even slower waves known as delta waves that exhibit high amplitudes and rhythmic continuity.

12)

A drug that blocks monovalent cation channels would affect skeletal muscle by preventing the movement of Ca2+ ions, which cause the release of acetylcholine and, through the process described above, activate the contraction of muscle fibers. Though calling such a drug a muscle relaxant might allow for a descriptive understanding of the drug's ultimate function, it does not accurately describe what the drug does, at elast not entirely. Stopping the diffusion of Ca2+ ions will of course reduce muscle potential, but the greatest effect of the drug is actually on the nervous system, where it prevents the action potential of the axon terminal from being transferred to the receptors at the motor end plate.

13)

The differences in concentration of ions creates the greater flux of Na+ ions; as the sodium-potassium pump pushes more Na+ ions outside of the cell in much greater concentrations than potassium ions, the extra incentive of diffusion in addition to the pull created by the depolarization and charge imbalance creates a much greater flux in Na+ levels.

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